Proton magnetic resonance detection of ionophor mediated transport of praseodymium ions across phospholipid membranes

Abstract

This study describes the use of proton magnetic resonance spectroscopy (PMR) to detect the penetration of paramagnetic cations into the internal compartment of lipid vesicles. It has been previously demonstrated that when a non-penetrating paramagnetic cation such as Pr 3+ is added to an aqueous lecithin dispersion, the proton magnetic resonance signal of the -N +(CH 3) 3 show two distinct peaks which arise from the groups in the inside and outside of the vesicles, respectively. When Pr 3+ is added to lecithin liposomes containing the ionophore X-537A, the PMR signal of the trimethylammonium protons, shows only one distinct peak. THis single peak is the result of the interaction of Pr 3+ with the -N +(CH 3) 3 groups of both the inner and outer layer of the liposome. This suggests that the antibiotic allows the diffusion of the lanthanide into the interior of the vesicle. Experiments performed in black lipid films show that indeed the ionophore makes the membrane permeable to Pr 3+, thus supporting the interpretation of the PMR data.